Recent research has found invertebrates to be useful tools in understanding aspects of reproductive biology, environmental toxicology and population genetics. The proposed research is intended to address questions related to the effects of environmental contaminants on biological systems At different levels of organization (subcellular, cellular, organismal and population), at different life history stages (fertilization, embryological development and settlement and metamorphosis of larvae) and on uptake of algal symbionts of mass spawning corrals. The proposed studies will be undertaken to test the following hypotheses: 1) Certain reproductive and life-history stages of corals are more sensitive to environmental toxins than others; 2) The incorporation of symbiotic algae into coral recruits is affected by both genetic and environmental factors: and 3) Biomarkers can be used to detect chemically-induced stress at sublethal levels. The three hypotheses will be tested using cells, eggs, sperm, larvae, and tissue from coral colonies both collected from the field and cultivated under controlled laboratory conditions. The effects of pesticides on gamete interactions, fertilization and embryological development are important questions of biomedical relevance. Organisms can respond to chemicals at levels below detectable limits, and may also bioaccumulate toxic substances. For this reason, bioassays with appropriate organisms are valuable tools for understanding and modeling the impacts of toxic substances on sensitive biological interactions and life-history stages. Data collected during this ongoing research can be applied to potential toxicological effects of xenobiotics on non-target organisms, including humans and as such have important implications for environmental and public health.